The ink jet recording method has rapidly developed and is spreading even now for the reasons that the materials are inexpensive, high speed recording is possible, the noise in the time of recording is low, and color recording is easy.
The ink jet recording method includes a continuous system of continuously ejecting ink droplets, and an on-demand system of ejecting ink droplets corresponding to image data signals, and the ejection system includes a system of ejecting ink droplets by the application of pressure with piezo elements, a system of ejecting ink droplets by the generation of foams in the ink by heat, a system of using ultrasonic waves, and a system of ejecting ink droplets by suction with electrostatic force.
As the ink jet recording ink, aqueous ink, oil ink or solid (melting type) ink is used.
The colorants for use in these ink jet recording inks are required to have good solubility or dispersibility in a solvent, to be excellent in a color developing property and capable of high density recording, to show good hue, to be fast to light, heat and active gases in the environment (oxidizing gases, e.g., NOx, ozone, etc., and SOx, etc.), to be excellent in fastness to water and chemicals, to be good in fixing ability to image-receiving materials and to hardly blot, to be excellent in preservability as ink, to be nontoxic, to be highly pure, and to be available inexpensively. However, it is extremely difficult to find colorants that satisfy these requirements on a high level. In particular, colorants for black ink having good black tone, capable of high density printing, and fast to light, humidity and heat are strongly desired.
Disazo dyes and trisazo dyes have been conventionally used as dyestuffs for black, but these dyes alone are not sufficient for absorption of blue and green lights to obtain good black tone in many cases, so that dyes for color correction of absorbing blue and green lights are generally used in combination. As such dyes for color correction, the dyes as disclosed in JP-A-9-255906 (the term “JP-A” as used herein refers to an “unexamined published Japanese patent application”) and Japanese Patent 3178200 are proposed to contrive to improve the adjusting ability of black tone, a color developing property, fastness, the preservation stability of ink, water tightness, and clogging of nozzles.
However, conventionally proposed dyes for color correction are too short in wavelength of absorption, and so they are wanting in the adjusting ability of black tone such that dyes must be added in quantities or other dyes for color correction are further necessary.
Although dyes capable of absorbing blue and green lights are generally known, these dyes are inferior in fastness, so that hue is largely changed by the exposure of an image to light, heat and active gases in the environment, and fixing ability is also insufficient. As a result, a phenomenon that the dye at the contour part bleeds in yellow inevitably occurs under high humidity condition, thus further improvement is necessary.
In consideration of these drawbacks, a black ink composition comprising a black dye having been blended with, as the dye for color correction, a triazine dye having the absorption maximum at 435 nm of the absorption spectrum in the visible region in an aqueous solvent is disclosed in JP-A-2002-332426.
However, general black dyes have the absorption maximum at 570 to 620 nm, so that, considering the relationship of complementary colors important for black tone adjustment, it is apparent that suitable black tone cannot be obtained even the dye for color correction is used (Shikisai Kagaku Handbook (Handbook of Color Science), the Second Edition, pp. 560-562, Publishing Association, The University of Tokyo (1998)).
C.I. Direct Red 84 is disclosed in JP-A-8-302255, but there is no description in the same patent about a black ink composition of using the dye as the short wave dye and combining with a long wave dye.
JP-A-2000-265099 discloses C.I. Direct Red 84 (paragraph 8), but as magenta, and there is also no description in the same patent about a black ink composition of using the dye as the short wave dye and combining with a long wave dye similarly to the above patent.
A black ink composition combined with a specific long wave dye is disclosed in JP-A-2005-146244.